(a) Field of the Invention
The present invention relates to a liquid crystal display and a driving device thereof.
(b) Description of the Related Art
A typical liquid crystal display (“LCD”) includes an upper panel provided with a common electrode and an array of color filters and a lower panel provided with a plurality of thin film transistors (“TFTs”) and a plurality of pixel electrodes. The two panels have respective alignment films coated thereon and a liquid crystal layer is interposed therebetween. The pixel electrodes and the common electrode are applied with electric voltages and the voltage difference therebetween causes electric field. The variation of the electric field changes the orientations of liquid crystal molecules in the liquid crystal layer and in turn the transmittance of light passing through the liquid crystal layer, thereby obtaining desired images.
A typical data driver of an LCD includes a shift register, a data register, a data latch, a digital-to-analogue (“D/A”) converter and an output buffer. The data driver latches red (“R”), green (“G”) and blue (“B”) data sequentially inputted in synchronization with a dot clock from a timing controller and alters the timing system from a dot-sequential scheme into a line-sequential scheme in to output data voltages to data lines of a liquid crystal panel assembly. The D/A converter converts the RGB data from the data latch into the respective analog voltages on the basis of gamma reference voltages VGMA1 to VGMA18 provided from an external device.
A normal LCD uses identical signals for R, G and B pixels assuming that their optical characteristics are the same, which are different in practice. As a result, there is a problem that the impression of colors for respective grays is not balanced or excessively biased.
To solve this problem, it is suggested to provide different sets of gamma reference voltages for respective R, G and B colors. However, this increases the number of pins of the data driver by thirty-six relative to the previous one and thus the size of the data driver. In addition, the unit for generating the gamma reference voltages has the increased number of blocks, i.e., three blocks for respectively generating corresponding sets of the gamma reference voltages for R, G and B colors. There is a problem that the increase of external circuits as well as the increase of the mounting area for the data driver in a printed circuit board (“PCB”) raises the production cost of the LCD.